Each year humans place an increasingly greater demand on the biosphere. The world's increasing level of industrialization has come to produce a surge in the consumption of natural resources, while at the same time producing an equally large amount of waste material that is either non-recyclable or simply not recycled. The replacement of metals by plastics in the last century somewhat abated the growth in the demand for this resource commodity. But with the rise in synthetic polymer technology, came an explosion in the use of synthetic polymers with the result that today plastics and other synthetic polymers are the most utilized category of non-naturally occurring materials.
Polymers, however, are ubiquitous in nature. These natural building blocks have been used by mankind since antiquity, for example, fibers made of hemp, cotton, wool, and silk are all a part of human development. Processes directed to the manufacture of articles comprising recyclable plant polymers such as cellulose, are well known and have been under development for many centuries. Less well studied are processes that utilize natural polymers derived from non-plant sources, i.e., the hard outer shells of marine animals.
Chitin is the most abundant polymer in the marine environment. Chitin is the main component of the exoskeletons of arthropods, such as crustaceans and in the cell walls of fungi. It has been a major source of surface pollution in coastal areas. Both chitin and its major derivative chitosan (obtained by deacetylation of chitin) have numerous applications. The bioactivity, biocompatibility, and low toxicity of native or chemically-modified chitin and chitosan make them suitable for controlled drug release, cosmetics, food preservation, fertilizer, or biodegradable packaging materials, or waste water processing and other industrial applications. Chitin, however, is highly hydrophobic and is insoluble in water and most organic solvents due to the high density of hydrogen bonds of the adjacent chains in solid state. The difficulty in the dissolution restricts the use of chitin as a replacement for synthetic polymers.
Crustacean shells are currently the major source of chitin available for industrial processing. The best characterized sources of chitin are shellfish (including shrimp, crab, lobster, and krill), oyster, and squids. Annual synthesis of chitin in freshwater and marine ecosystem is about 600 and 1600 million tons, respectively. Producing chitin in industry is primarily from the exoskeletons of marine crustacean shell waste by a chemical method that involves acid demineralization, alkali deproteinization, and followed by decolorization. Even though the current industrialized chemical process isolates chitin from crustacean shells efficiently, disadvantages exist in these procedures, including, inter alia, the use of corrosive acids, bases, and strong oxidants which are not environmentally friendly. In addition, these processes can modify or nullify the desired physiochemical properties of chitin, for example, by acid demineralization, shorting the chitin chain length, as well as, degrading the chitin during deproteinization in hot alkali solutions. These undesired changes in the properties of chitin can have a profound affect when the chitin obtained therefrom must have specific molecular weight distributions and degrees of acetylation (DA).
As such, there is a long felt need for films, fibers, and beads formed from chitin wherein the chitin has both consistent, as well as, desirable properties. There is also a need for chitin compositions that can be efficiently and reproducibly manufactured under environmentally friendly and mild conditions. Disclosed herein are processes and compositions that address these and other needs.